EFFECT OF SCREENING ON POSITRON ANNIHILATION CHARACTERISTICS IN METALS

Abstract

A screening parameter was introduced into the enhancement factor used to calculate positron annihilation rates based on the perturbed hypernetted chain approximation model. The consequential effects of electron-positron screened pseudopotential on positron annihilation rates in metals were thereby studied. The results obtained for the annihilation rates were in very satisfactory agreement with experimental values for alkaline, alkaline- earth, some transition and noble metals. It was also revealed that high annihilation rates were recorded in metals in which the electron-positron screened pseudopotential is small and vice-versa. The study further revealed that electron-positron correlation energy due to screening in metals decreases the total electron-positron correlation energy (as it has a smaller value than the total electron-positron correlation energy) and it varies in the same manner with the eleq;on gas parameter as the electron-positron correlation energy. On the total potential experienced by positrons in metals, the study showed that electron-positron correlation potential has the minimum contribution to the total potential and it increases with an increase in the electron gas parameter. Also, the total potential has the highest contribution from the electronic potential for alkaline, alkaline-earth and simple metals while the highest contribution for transition metals is from the ionic potential. From the study. an interpolation expression was put forward for calculating the total potential experienced by positrons in metals.